а) 15:10=x:40; г) х: 1 1/3=6:4; б) 3,6:4,2=6:х; д) х: 3,86=2,5:2 1/2. в) 3:х=3/8:1/4;

№1

15 : 10 = х;

х = 15 : 10;

х = 15/10;

х = 1 5/10;

х = 1 1/2.

Проверка:

15 : 10 = 1 1/2;

15/10 = 1 1/2;

1 1/2 = 1 1/2.

№2

х: 1 1/3 = 6 : 4;

х: 4/3 = 6/4;

х * 3/4 = 6/4;

х * 3/4 * 4/3 = 6/4 * 4/3;

х = 24/12;

х = 2.

Проверка:

2 : 1 1/3 = 6 : 4;

2 : 4/3 = 6/4;

2 * 3/4 = 6/4;

6/4 = 6/4.

№3

3,6 : 4,2 = 6 : х;

3 6/10 : 4 2/10 = 6 : х;

36/10 : 42/10 = 6 : х;

36/10 * 10/42 = 6 : х;

36/42 = 6 : х;

6/7 = 6 : х;

х = 6 : 6/7;

х = 6 * 7/6;

х = 7.

Проверка:

3,6 : 4,2 = 6 : 7;

36/10 : 42/10 = 6/7;

36/10 * 10/42 = 6/7;

36/42 = 6/7;

6/7 = 6/7.

№4

х: 3,86 = 2,5 : 2 1/2;

х: 3 86/100 = 2 5/10 : 2 1/2;

х: 386/100 = 25/10 : 5/2;

х: 386/100 = 25/10 * 2/5;

х: 386/100 = 50/50;

х: 386/100 = 1;

х * 100/386 = 1;

х * 100/386 * 386/100 = 1 * 386/100;

х = 386/100 = 3 86/100 = 3 43/50.

Проверка:

386/100 : 386/100 = 2,5 : 2 1/2;

386/100 * 100/386 = 25/10 * 2/5;

1 = 1.

№5

3 : х = 3/8 : 1/4;

3 : х = 3/8 * 4/1;

3 : х = 12/8;

х = 3 : 12/8;

х = 3 * 8/12;

х = 2.

Проверка:

3 : 2 = 3/8 : 1/4;

3/2 = 12/8;

3/2 = 3/2.